Here's Tom Cruise as a hair-metal god and hair metal as un-awful in Rock of Ages

Rock of Ages, a new star-clogged pop-musical diversion, is a cinematic event. It's not every day, after all, that you get to see two great American traditions — guitar/bass/drums rock music and Tin Pan Alley musical theater — so thoroughly, mutually degraded.

Like Mamma Mia! or Jersey Boys, it belongs to the species that has been dubbed the "jukebox musical," in which a group of licensed pop songs are strung together to create a ready-made musical score. This practice of steering a story between preexistent tunes effectively guarantees that the songs cannot grow from the plot organically, while challenging the author of the book to invent the pretext of a narrative setting in which to imbed the numbers.

It's West Hollywood, 1987, and a bus pulls up to a corner to disgorge Julianne Hough, here playing Sherrie, a girl from Tulsa dreaming of the big time as a frontwoman. Instead, she gets her suitcase stolen and ends up waiting tables at the Bourbon Room, thanks to the intervention of young Drew (Diego Boneta), who we know is destined for Sherrie, as he shares her scruffily clean-cut looks, her wide-eyed Juke Box Hero aspirations, and is, like her, staggeringly dull.

Even this safe haven is not, however, safe. "Taxes, they're so un-rock & roll," Bourbon owner Dennis (Alec Baldwin) sighs, faced with a money-crunch deadline as the mayor's anti-rock crusader wife, Patricia Whitmore (Catherine Zeta-Jones), scrutinizes the Bourbon's fudged books, looking for any excuse to shut the place down as part of her "Clean Up the Strip" initiative. Dennis' Hail Mary solution is corralling back Stacee Jaxx (Tom Cruise), former Bourbon mainstay turned decadent, dissipated and totally unreliable arena rocker, for a one-off benefit show.

Cruise has the advantage of playing one of those built-up parts: Everyone in the first act talks up Stacee Jaxx, so he can't help but be impressive by the time he shows up. The dissolute rock-god gags are old hat, but Cruise is a dynamic, kabuki-esque, full-body performer, and he gives Jaxx something between the boozy silverback swagger of Jim Morrison and Glenn Danzig's armored-car physical presence.

Jaxx finds his match in Malin Akerman's Rolling Stone reporter, who calls out Jaxx's coasting career under Paul Gill (Paul Giamatti), his manager. Gill says things like "We did a whole focus group on this — numbers don't lie" (which probably tested well) and will later get his hooks into rising star Drew, drafting him in a New Jack Swing–style boyband. This is presented as the epitome of sellout, which only makes sense if you are willing to accept the premise that there was more artistic integrity in being a member of, say, Poison, than in being in New Kids on the Block.

There are two basic ways of thinking about this music; which one you're inclined toward will probably influence your enjoyment. One is fond nostalgia — this was innocently hedonistic good-time party music, with hooks big enough to land Moby-Dick. "Goddamn, they don't make 'em like they used to," said Mickey Rourke's Randy "The Ram" in The Wrestler, when Def Leppard comes on in a bar. "Then that Cobain pussy had to come around and ruin it all."

The other — which I happen to believe — is that that Cobain pussy did everyone a great favor, because hair metal was bone stupid, creatively bankrupt, morally debased pop trash that marked an all-time low in record-label-chart manipulation and synthetic hit-making hackery. And if rock, as is herein insisted, will never die, the "rock" paradigm perpetuated by Rock of Ages — the same as in Rockstar energy drink and Nickelback's "Rockstar" and the Hard Rock Hotel & Casino in Hollywood, Florida — deserves a deep, dank unmarked grave.